Composite structure



t Y k given bya solution in benzene of plasticised acrylic acid United States Patent 2,982,681 M COMPOSITE STRUCTURE H Edward Crampse y, Dennis Grady, and Philip. Richard Hawtin, all of Spondon, near Derby, England, assign- ,ors to British Celanese Limited, a corporation of Great v l 'i a NoDi-awing. Filed Dec. 30, 1957, Ser. No. 705,142 v priority, application .Great Britain Jan. 11, 1957 5 'Claims.- (Cl. 154-46) This invention relates to polymers, and especially to copolymers of vinyl acetate, and to adhesives based on the said copolymers, and their use in bonding cellulose ester film to printed paper.

.. v..Considera-ble .difliculty has hithertobeen experienced in a suitable adhesive for bondingthin films of ','cel lulosev,aeetate. or {other organic ester of cellulose to ,1 heavily printed paper attemperatures belowthesoftening' f the film laymethods capable; ofv being runjcorn an minute. An adhesive for purposemust be sufficiently soft andtacky duringthe bonding operation to form a uniform coating over the film; it must adhere to the film, .4 e rarer-a d th k- Q 'i-t Paper; i m be tr w an .flexible at-ordinary-temperatures and must remain printed p t r-l n Pe ds;-

I i I V L ned above, very: many combinations of various polyn ers, including polymersandcopolymers of vinyl acetate andof. acrylic acidesters, with single and mixed plastic'iSersIsorhe compatible. with the cellulose ester, some with the polymer and some with printing ink binders, N were investigated, but with very little success. By careful fgrngulationit'was foundpossible to obtain sufliciently z gogd; initial; adhesion but on storage the adhesion was found to fall 01f, aceompanied usually by the development of brittleness either in th e film or the adhesive or both. This loss of adhesion and development of brittlenessapshea ed-ta bedue ta m r tio z f,plasticiser,from thefil into the adhesive and/9r fromtheadhesive into the film or into the ink. With a'n adh 'sive based on a copolymer of] vinyl chloride, vinyl ac'e'fat'e'and maleic'anhydride, for

;.--in ance;iplasti ise mwi h a: mixture otidibuty p and trichlorethyl phosphate and dissolved in a mixture of toluene and methyl ethyl ketone a satisfaetory initial adhesion was obtained but adhesio several months owing apparently to gratiodpf plasticiser from the esive atcths l. Ma at mi were made, by incorporating in the adhesive a proportion or 'plasticisen of 'slower compatabilitywithithe' cellulose ea'c'etate; tof-bbtain an adhesive that did notsufier from :this'f defe'ct, but? all these attempts :were. unsuccessful.

aiUntiLthe present' inv'entioniwas made the nearestsapproach to success. after several years .work on rthe lproblenr "1 copolymer. This compositiom'however, had obvious dis-1.

R advantages. One of these was"the' toxic nature; of the flsolvent. {It was foundimpossible to replac'e this by a l fion toxic solvent without either weakening-the adhesion 'o'btainedon damaging the Finally; it found that excellent long-term adhesion could. be obtained by-Y of plasticiseranddissolvedin anon-toxic volatiletsolvent, T such as isopropanol, or isopropyl acetate, which does not at relatively high speeds, eg. 3 10 metresper al 1d it must retain its. adhesion to the film and the attem n t sa if' th exacting u men P t nt May 2 1961 adversely atfect'cellulose acetate film. ,Moreo'v'er, adhesives having a basisof the copolymer canbe used in bond- ,ing films of other thermoplastic substitution derivatives oficellulose to ,printed surfaces, especiallyfsurfacesfof 5 cellulose (including regenerated cellulose). "The invention includes broadly structures comprising a filni ofj,a thermoplastic substitution .deriv-ative'of cellulose bonded to a printed surface by means of an adhesive havingga basis of a copolymer of vinyl acetate and a dibutyl maleate, said copolymer containing to by Weight 7 of combined vinyl acetate. r 1

In the composite structures of the invention those in which the cellulose derivative is a celluloseester of a paraffinic monocarboxylic acidcontaining 2 to 4 carbon atoms, and especially those in which the cellulose ester is cellulose acetate, are .of most importance. Thermoplastic substitution derivatives other than cellulose acetate ,from which the film employed in, such structures can be made includezjherinoplastic organic esterssuch as cellu- 20.,lose'v propionate, j cellulose? butyrate, cellulose acetatepropionate, cellulose acetate-butyrate, andthermoplastic Q cellulose .ethe'rs such as ethyl cellulose, as well ascellulose (nitrate. Q .1 l IThe printed surface mustlof course be onefor which 25, fa.suitablefprintingjink can be f formulated andto hich the copolymer adheres. The. surface may, for instance, be that. of aluminum foil oro'f rubber hydrochlorid for. may be a' surface of polythene rendered.receptiv to printing, elgi by an electrical corona"dischargtreatmeht 30. or by a'flarne treatment. Of particular importance,;how-

surface is'of cellulose (including regenerated cellulose). Such .a cellulose surface may, for, instance, be .that' pf paper, cardboard or other'paper-likei'product havingia jbasis of cellulose fibres, or of a film of 'jre'generatedflcellnlose. These surfaces, in contrast say with the surfaceof textile fabrics, may be termed unitary surfaces? ifijthat though they maybe formed of fibres, as inl' papenithey are not formed'bynumer'ous independentlyv movab 40 ments of-surfaeeL. It is With'such unitary surface s a y whensm h as .fi ms,1-m l jr 1 1 fed of the adhesives of the invention shows tomost advantage. The termfiprinted surface is to be regarded as meaning 1 a, surface to'ce'rt areas only of whieh there has been asp red (in any ma vehiclecoiitaining a binder. s

In the copolymer forming, the; basis of the adhesive the dibutyl maleate is preferably. the di-n-butyl or di-isobutyl ester. 7

A11 adhesive p ic rly sui ab ic d nsfi m; 10 cellulose acetate containing 52jto 516% ofcornbined acetic acid to printed papercornprises a copolymer or i specified above in solution in an alcoh l or este 55 below '100? C; which is not a solvent or'strong s agent' for such cellulose acetate. The solvent may fpr example be a saturated aliphatic alcohol containing'Zf'to j 3 carbon atoms, especially commerciallethanol or iso- I propanol. "(The term isopropanol f throughout the speciggjjfication is used o meanthe azeotropic mixture with water f; sold co n is'opropy1acetate. v I In the preferred method of, making the adhesives-of v the invention the copolymer is'made by, bulk polymerisation initiated.) by" .a; free-radical: polymerisation initiator thatis soluble. inzthefmonomet'niixtylre and after. at least 975% ,ofithe monomer mixt'urefhas polymerisedthessolventismixed Witlhthe. polymento form a solution .th'etef yof. Hnwgeneral polymerisationcan-gbe carried, a far zaps- 0% or even@=- .5.%. ccnversiontbased .ongtotal monomer) without 7 undue jdifiiculty ini. StiITi tgqQ wirtheiabsence of solvent, but as polymerisationcontinues ever, are composite structures in which, the ink, printed yiagwnteb ack r c nn d Pigmen g 3' the great increase in viscosity calls for a progressively "increasing expenditure of power in stirring. It has been found best, therefore, to add solvent after 75 to 85% conversion. Further polymerisation. can then be effected, e.g. to '90%f or even to 95%"conversion, andwith a view. to "so increasing the conversion additional initiator inaylbe added 'with the solvent; 'The additional poly- "mer formedafter the additionof solvent islikely, to be I, jjofm u'ch lower. average molecular weight than that formed Z'before the addition, especially when thegsolvent has fa strong chain-transferaetion as have the alcohols. The presence of the'low molecular fraction, however, does .not appear disadvantageous and it may function advantageously as a plasticiser. Onflthe other hand, an'undue proportionof low molecular polymer may give the solution a lower" viscosity. than is required. It might be thought that this could easily .be remedied by adding a proportion of'copolymer of high molecularweight, i.e.

of intrinsic viscosity at least 0.5, e.g. 0.5 to 0.6, made v to low conversion. (Intrinsic viscosities referred to in L this'specification are determined in 1% solution in commercial isopropanol atj25 C.) We have found however, that such addition maycausje separation into two phases, but that if the high molecular weight copolymer be 'present in solution in the initial monomer mixture 'a homogeneous solution of relatively high viscosity can be obtained even when the last portion of copolymer formed is of substantially lower averagemolecular weight. than that formed before the addition of solvent. It is fof advantage for the viscosity of the solution finally obftain'ed to be in the range 450 to 550 cps., e.g. 500 to 525 cps., at C. Toobtain such solutions of suitable con- "eentration, i.e. 20 to45% and preferably 20 to 30%, it i 1 is desirable for the'intrinsic viscosity of the copolymer tobe within the range 0.45 to 0.55. The initiator used in' the polymerisation may be an organic peroxy compound soluble in the monomer mixture, e.g. benzoyl peroxide or lauryl peroxide, or a -monomer soluble'azo-di-nitrile e.g. azo-bis-isobutyronitri1e., V

If'desir'ed a plasticiser for cellulose acetate may be incorporated in the solution. Suitable plasticisers in- "clude: di-methoxyethyl phthalate, tri-(2-chlorethyl) phos- ,phate, t-riphenyl phosphate and chlorinated diphenyl. The proportion of plasticiser should be relatively low, e.g. '10 to 20% and preferably 10 to 15%, of the Weight ,of the polymer. 7 The following examples illustrate the invention. In

f the examples, and throughout-the specification unless o'therwise stated, all parts and percentages are by weight.

. ,1 Example 7 1 The charge was as follows: f 250 parts of di-n-butyl maleate.

2 parts'of vinyl acetate. 1 f 1.25 parts of benzoyl peroxide.

.charge wasrun into a polymerisation vessel'pro! J'vided with robust stirring means, inlet for nitrogen and frefiux-condenser, after flushing the vessel out with nitrojgenQ The ,charge' was. heated at -80 C. under an atmosphere of nitrogen for 40 hours. The polymer so formed was .dissolved in situ by runninginto the vessel 600.parts of commercial isopropanol (containing 10% of water) and continuing the stirring'until solution was complete. v q

- Fema 2 1.

r Ihe process was carried out as described in -Example -1 except that: only '05 part of benzoyl peroxidewere employed, the,polymerisation was :carried out at to. --'-85 6., and the isopropanol was added after thepolymerisation' had been continued for-9 hours. The ionw approximately versionk-(based ontotal rnonomercontent) 'at thisstage 5*. ":jjfl

' propanol.

0.02 part of azo-bis-isobutyronitrile. a

- Polymerisation was carried out at a.-te'mperature.of 80' Crfor 24 hours by which timethe' conversion; based-on .total monomer,-.was 84%. The reaction mixture'fwas-s 4 Example 3 A reaction mixture of the following composition was made:

50 parts of vinyl acetate.

50 parts of di-n-butyl maleatei 7.

0.1 part of azorbis-isobutyronitrile.

, Into a vitreous-enamel lined vessel with reflux condenser and enamelledstirrer, and heated to 80 C. by ,meansof fa steam jacket, 50 parts of the reaction mixture was Example 4 v The process was carried out as in Example 3except that: there was added with the 20 parts of isopropanol "(first addition) an additional" 0.1 :partof Jazo-bis-isobutyronitrile 'and the heating wasimain tained for 2% hours'after finishing thisaddition and .before discharging Y the reaction mixture." The conversion was then "f% based on the initial total monomer. I

Example 5 35 parts of polyvinyl acetate or high molecular weight were dissolved in 65 parts of'vinyl acetate. 38 parts of this solution were mixed with 25 partsof di-n-butyl maleate and 0.2 part of benzoyl perdxide. The mixture "was polymerised for 24 hours "at 80 to 81 (2., by which time the conversion was 95% based on the total monomer. The product gave a smooth solution in commercial-iso- A 21% solution of the polymer in isopropanol had a viscosity of 503 cps.

Example 6 The process was carried out as in Example 4 except '1 -thatindustrial ethanol was used instead of isopropanol so obtaining a more volatile solution.

. E a l The process'was carried out'asin Example 4-b t isopropyl acetate instead of the isopropanol. :1 f v Jae-awa t.

A reaction mixture ofithe following compositionwas prepared:

10 parts of di-isobutyl male'ate.'- 1 0, partsof vinyl acetate.

4 parts of. isopropyl acetate.

cooled and. diluted with additional isopropyl 'acetatel to 'wehwas a heavily printed glazed: paper. 'The bonding' was effected on a film laminating machine givea solution containing 22% byw'eight of solids.

*JExample'Sl j a This example illustrates the bonding. a

Thefilm employed was 1 mil thick and composedpf. cellulose acetate containing 52 to 54% combined acetic acid plasticised. with a mixture o f-diethyl phthalate and The printedtriphenyl phosphate, in the, ratio of 3:1,

in which. the filniis drawn from a spoolinto contact with aa-fmnishing rolldippingjinto a trough of the adhesive,

and from t e: sid

there runs up onefside 'and down-theo of a drying tower and then through the nip of a pair of horizontal rolls where it is bonded to the printed paper and the laminate then passes to a take-up roll. The upper nip roll is of nickel plated steel and is heated by hot water. The lower nip roll is covered with synthetic rubber and is urged towards the upper roll by hydraulic pressure. The paper fed into the nip is slightly wider than the film to avoid any contact of the coated surface of the film with the rolls.

In effecting the bonding the adhesive trough was fed with the copolymer solution obtained by one of the processes of Examples 1 to 8; the drying tower was sup plied with a current of air at a temperature between 60 and 80 C. according to the volatility of the solvent, the speed of the machine was adjusted so that the coating on the film was substantially dry on leaving the tower; and the upper nip roll was heated to a temperature between 60 and 70 C.

With all the solutions of Examples 1 to 8 good adhesion was retained both to the printed and unprinted parts of the paper after three months storage. There was a slight tendency of the laminates to curl but this was not considered serious.

Examples 10 to 17 There was mixed into the solutions of Examples 1 to 8 respectively based on the weight of copolymer, of di-methoxyethyl phthalate.

When used in the process of Example 9 each of these solutions gave equally good adhesion accompanied by reduced tendency to curl.

Examples 18 to 25 These examples were carried out as Examples 10 to 17 respectively but using instead of the di-methoxyethyl phthalate a 50% mixture of this with chlorinated diphenyl. The tendency of the laminate to curl was reduced.

6 1 Examples 26 to 33 These examples were carried out as Examples 18 to 25 respectively but substituting triphenyl phosphate for chlorinated diphenyl. The tendency of the laminate to curl was reduced.

Having described our invention, what we desire to secure by Letters Patent is:

1. A composite structure comprising a film of a cellulose ester of a paraffinic monocarboxylic acid contain ing from 2 to 4 carbon atoms in the molecule and an inkprinted surface, the said film and said printed surface being bonded together by means of an adhesive having a basis of a copolymer of vinyl acetate and an ester chosen from the group consisting of di-n-butyl maleate and diisobutyl maleate, said copolymer containing 35 to percent by weight of combined vinyl acetate.

2. A composite structure as claimed in claim 1 wherein the printed surface is a unitary surface of cellulose.

3. A composite structure as claimed in claim 2 wherein the printed surface is of paper.

4. A composite structure as claimed in claim 1 wherein the cellulose ester film is a cellulose acetate film.

5. A composite structure as claimed in claim 4 wherein the adhesive also includes a plasticiser for cellulose ace- 7 tate chosen from the group consisting of di-methoxyethyl phthalate, tri-phenyl phosphate and chlorinated diphenyl.

References Cited in the file of this patent UNITED STATES PATENTS 1,972,448 Jenkins Sept. 4, 1934 1,983,870 Ostwald Dec. 11, 1934 2,137,636 Barrett Nov.,22, 1938 2,200,437 Voss May 14, 1940 2,410,089 Lundquist et al. Oct. 29, 1946 2,430,564 Gordon Nov. 11, 1947 FOREIGN PATENTS 581,473 Great Britain Oct. 14, 194 

1. A COMPOSITE STRUCTURE COMPRISING A FILM OF A CELLULOSE ESTER OF A PARAFFINIC MONOCARBOXYLIC ACID CONTAINING FROM 2 TO 4 CARBON ATOMS IN THE MOLECULE AND AN INKPRINTED SURFACE, THE SAID FILM AND SAID PRINTED SURFACE BEING BONDED TOGETHER BY MEANS OF AN ADHENSIVE HAVING A BASIS OF A COPOLYMER OF VINYL ACETATE AND AN ESTER CHOSEN FROM THE GROUP CONSISTING OF DI-N-BUTYL MELEATE AND DIISOBUTYL MALEATE, SAID COPOLYMER CONTAINING 35 TO 50 PERCENT BY WEIGHT OF COMBINED VINYL ACETATE. 